Methods of altering the refractive index of materials

ABSTRACT

Methods and devices for altering the power of a lens, such as an intraocular lens, are disclosed. In one method, the lens comprises a single polymer matrix containing crosslinkable pendant groups, wherein the polymer matrix increases in volume when crosslinked. The lens does not contain free monomer. Upon exposure to ultraviolet radiation, crosslinking causes the exposed portion of the lens to increase in volume, causing an increase in the refractive index. In another method, the lens comprises a polymer matrix containing photobleachable chromophores. Upon exposure to ultraviolet radiation, photobleaching causes a decrease in refractive index in the exposed portion without any change in lens thickness. These methods avoid the need to wait for diffusion to occur to change the lens shape and avoid the need for a second exposure to radiation to lock in the changes to the lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/876,909, filed Sep. 12, 2013. That application is hereby fullyincorporated by reference herein.

BACKGROUND

The present disclosure relates to methods and devices that are usefulfor adjusting the optical power of a lens. Such optical lenses mayinclude lenses in eyewear that are exterior to the eye and ophthalmiclenses that are used in close proximity to the eye.

The eye can suffer from several different defects that affect vision.Common defects include myopia (i.e. nearsightedness) and hyperopia (i.efarsightedness). These types of defects occur when light does not focusdirectly on the retina, and can be corrected by the use of correctivelenses, such as eyeglasses or contact lenses.

In particular, the lens of the eye is used to focus light on the retina.The lens is usually clear, but can become opaque (i.e. develop acataract) due to age or certain diseases. The usual treatment in thiscase is to surgically remove the opaque lens and replace it with anartificial or intraocular lens.

It can be desirable to be able to adjust such lenses, either before theyare provided to a user or afterwards. In the case of eyeglasses and/orcontact lenses, this permits the economical manufacture of lenses whichcan then be custom-fitted or adjusted to correct manufacturing defects.Such adjustments can also be useful in correcting misplacement of anintraocular lens during the surgical operation and/or to treat higherorder optical aberrations. A common method is to use ultraviolet (UV)activation to induce the change in lens performance, to allow for highspatial resolution of the adjustment (due to the low wavelength of UV).After the lens is adjusted, the lens should not appreciably change inperformance over the lifetime of the lens.

U.S. Pat. No. 7,134,755 describes a lens that uses ultraviolet lightcurable monomers in a silicone polymer matrix. The monomers areselectively polymerized using a digital light delivery system to alterthe lens power at specific points.

There are two distinct effects that alter the lens optical power in thissystem. First, the polymerization of the UV curable monomers changes therefractive index of the system from n=1.4144 to n=1.4229, which wouldincrease the optical power of the test lens from 95.1 diopters to 96.7diopters. This change in the lens power is much smaller than the changein lens power that was reported in the patent, indicating this is notthe primary mechanism of index change in this patent.

The second effect, which is responsible for the largest component of thechange in lens optical power, is a swelling of the lens in theirradiated region. This swelling effect is illustrated in FIG. 1.

In FIG. 1A, free monomers (denoted M) are present in a silicone polymermatrix 10. In FIG. 1B, a mask 20 is used to expose only a portion 30 ofthe lens to UV radiation. The monomers in the region exposed to the UVradiation undergo polymerization, forming polymers P and slightlychanging the refractive index. Over time, as seen in FIG. 1C, monomersfrom the un-exposed regions 40, 50 then migrate into the exposed region30, causing that region to swell. This change in the lens thickness thenleads to a larger change in the optical power. In FIG. 1D, after themigration of the monomer is finished, the whole lens is then exposed toUV radiation to freeze the changes.

There are several shortcomings to this method. One is that the primarychange in the lens optical power is due to diffusion of monomer, whichis a relatively slow process. Another shortcoming is that the dependenceon diffusion as the operative effect limits the spatial resolution ofthe changes in the lens optical power. A third shortcoming is that theincrease in lens thickness in the exposed region forces a thicknessdecrease in adjacent regions, as monomer from the adjacent regiondiffuses into the exposed region. This change in thickness in theadjacent regions is not easily controllable. Lenses without theseshortcomings and others are desirable.

BRIEF DESCRIPTION

Disclosed in various embodiments are devices and methods for adjustingthe optical power of a lens. Among other benefits, these lenses do notcontain free monomers, so there is no change in lens shape due todiffusion of monomers. There is also no need for a second UV radiationexposure of the total lens to “lock-in” the refractive index changes.

Disclosed in some embodiments is a lens comprising: a single polymermatrix having crosslinkable pendant groups, wherein the polymer matrixincreases in volume when crosslinked; and wherein substantially no freemonomers are present therein.

The lens may further comprise a UV absorbing layer on at least onesurface of the lens.

The pendant group may be3,9-divinyl-2,4,8,10-tetraoxy-spiro[5.5]undecane.

Disclosed in other embodiments is a lens comprising a polymer matrixincluding photobleachable chromophores.

The photobleachable chromophores may be dispersed within the polymermatrix, or be present as pendant groups on the polymer matrix.

At least one chromophore may comprise a reactive site which cancrosslink with a reactive site on the polymer matrix.

The photobleachable chromophores may comprise chromophores containing amalononitrile moiety, such as those of Formula (I) or Formula (II):

Alternatively, the photobleachable chromophores may comprise stilbenechromophores of Formula (III):

where R₁-R₁₀ are independently selected from hydrogen, alkyl,substituted alkyl, aryl, substituted aryl, —COOH, and —NO₂.

Alternatively, the photobleachable chromophores may comprise azobenzenechromophores of Formula (IV):

where R₁₀-R₂₀ are independently selected from hydrogen, alkyl,substituted alkyl, aryl, substituted aryl, —COOH, —NO₂, halogen, amino,and substituted amino.

In other embodiments, at least one chromophore must absorb more than onephoton for photobleaching of the chromophore to occur.

Disclosed in still other embodiments is a method of altering the opticalpower of a lens, comprising: providing a lens comprising: a singlepolymer matrix having crosslinkable pendant groups, wherein the polymermatrix increases in volume when crosslinked; and wherein the lens isdevoid of free monomers; and exposing a portion of the lens toradiation, causing crosslinking to occur in the exposed portion of thelens and changing the refractive index of the exposed portion of thelens, thereby altering the optical power of the lens.

The exposed portion of the lens may be in the center of the lens. Theradiation to which the lens is exposed may have a wavelength of fromabout 200 nm to about 600 nm.

In other embodiments is disclosed a method of altering the optical powerof a lens, comprising: providing a lens comprising a polymer matrixhaving photobleachable chromophores; and exposing a portion of the lensto radiation, causing photobleaching to occur in the exposed portion ofthe lens and changing the refractive index of the exposed portion of thelens, thereby altering the optical power of the lens.

These and other non-limiting aspects and/or objects of the disclosureare more particularly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings, which arepresented for the purposes of illustrating the disclosure set forthherein and not for the purposes of limiting the same.

FIGS. 1A-1D are illustrations of a conventional method for adjustinglens optical power.

FIG. 2 is a graph showing a normalized change in lens optical power as afunction of the refractive index of the lens in both air and water.

FIGS. 3A-3B are illustrations of one method of the present disclosurefor altering the optical power of a lens.

FIG. 4 is a graph showing the change in the refractive index as afunction of the change in the volume of a polymer used to make the lens.

FIG. 5 is a graph showing the change in the lens optical power as afunction of the change in the volume of a polymer used to make the lens.

FIGS. 6A-6B are illustrations of another method of the presentdisclosure for altering the optical power of a lens.

FIG. 7 is a graph of the solar spectrum, showing the amount of energy ateach wavelength.

FIG. 8 is a graph showing the photon flux and the chromophore lifetimeas a function of the wavelength.

FIGS. 9A-9C are three figures describing bleaching via two-photonabsorption by a chromophore.

FIG. 10 is a cross-sectional view of an exemplary embodiment of a lensof the present disclosure.

FIG. 11 is an idealized transmission spectrum for a UV radiationabsorbing layer of the present disclosure.

FIG. 12 is a graph showing the refractive index of a lens as a functionof the amount of time the lens was exposed to UV radiation.

FIG. 13 is a graph showing the transmission spectrum of a contact lensbefore application of a chromophore, before bleaching, and afterbleaching.

DETAILED DESCRIPTION

A more complete understanding of the processes and apparatuses disclosedherein can be obtained by reference to the accompanying drawings. Thesefigures are merely schematic representations based on convenience andthe ease of demonstrating the existing art and/or the presentdevelopment, and are, therefore, not intended to indicate relative sizeand dimensions of the assemblies or components thereof.

Although specific terms are used in the following description for thesake of clarity, these terms are intended to refer only to theparticular structure of the embodiments selected for illustration in thedrawings, and are not intended to define or limit the scope of thedisclosure. In the drawings and the following description below, it isto be understood that like numeric designations refer to components oflike function.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). When used with a specificvalue, it should also be considered as disclosing that value. Forexample, the term “about 2” also discloses the value “2” and the term“from about 2 to about 4” also discloses the range “from 2 to 4.”

References to ultraviolet or UV radiation should be understood asreferring to the portion of the light spectrum having wavelengthsbetween about 400 nm and about 10 nm.

The “refractive index” of a medium is the ratio of the speed of light ina vacuum to the speed of light in the medium. For example, therefractive index of a material in which light travels at two-thirds thespeed of light in a vacuum is (1/(⅔))=1.5.

The term “chromophore” refers to a chemical moiety or molecule that hasa substantial amount of aromaticity or conjugation. This aromaticity orconjugation acts to increase the absorption strength of the molecule andto push the absorption maximum to longer wavelengths than is typical formolecules that only have sigma bonds. In many cases this chromophorewill act to impart color to a material. As defined here, the chromophoredoes not need to absorb in the visible (i.e. does not need to becolored), but can have its absorption maximum in the UV. Alternately,the chromophore could have absorption maximum in the near-IR, with nosignificant absorption in the visible wavelength range. The chromophorehas refractive index larger than that of the base polymer.

Non-limiting examples of chromophores which act to impart color to amaterial include C.I. Solvent Blue 101; C.I. Reactive Blue 246; C.I.Pigment Violet 23; C.I. Vat Orange 1; C.I. Vat Brown 1; C.I. Vat Yellow3; C.I. Vat Blue 6; C.I. Vat Green 1; C.I. Solvent Yellow 18; C.I. VatOrange 5; C.I. Pigment Green 7; D&C Green No. 6; D&C Red No. 17; D&CYellow No. 10; C.I. Reactive Black 5; C.I. Reactive Blue 21; C.I.Reactive Orange 78; C.I. Reactive Yellow 15; C.I. Reactive Blue 19; C.I.Reactive Blue 4; C.I. Reactive Red 11; C.I. Reactive Yellow 86; C.I.Reactive Blue 163; and C.I. Reactive Red 180.

Additional molecules which could act as a chromophore for thisdisclosure, but will not impart color to a material, include derivativesof oxanilides, quinones, benzophenones, benzotriazoles,hydroxyphenyltriazines, and other polyaromatic molecules. Other examplescan be found in Dexter, “UV Stabilizers”, Kirk-Othmer Encyclopedia ofChemical Technology 23: 615-627 (3d. ed. 1983), U.S. Pat. No. 6,244,707,and U.S. Pat. No. 4,719,248.

Other molecules which can act as chromophores for this disclosureinclude unsaturated molecules found in nature, such as riboflavin,lutein, b-carotene, cryptoxanthin, zeaxanthin, or Vitamin A, asexamples.

The term “photobleaching” refers to a change in the chromophore inducedby photochemical means. Exemplary changes may be the cleavage of thechromophore into two or more fragments, or a change in the bond order ofone or more covalent bonds in the chromophore, or a rearrangement of thebonds, such as a transition from a trans-bonding pattern to acis-bonding pattern. Alternately, the change could be the cleavage of abond such that the chromophore is no longer covalently bound to thepolymer matrix, allowing the chromophore to be removed during washsteps.

The term “optical lens” is used herein to refer to a device throughwhich vision can be modified or corrected, or through which the eye canbe cosmetically enhanced (e.g. by changing the color of the iris)without impeding vision. Non-limiting examples of optical lenses includeeyewear and ophthalmic lenses. The term “ophthalmic lenses” refers tothose devices that contact the eye. Examples of ophthalmic lensesinclude contact lenses and intraocular lenses. Examples of eyewearinclude glasses, goggles, full face respirators, welding masks, splashshields, and helmet visors.

The optical power of a simple lens is given by the following Equation 1:

$\begin{matrix}{\frac{1}{f} = {\left( {n - n_{0}} \right)\left\lbrack {\frac{1}{R_{1}} - \frac{1}{R_{2}} + \frac{\left( {n - n_{0}} \right)d}{n\; R_{1}R_{2}}} \right\rbrack}} & (1)\end{matrix}$

where 1/f is the optical power of the lens (measured in diopters orm⁻¹), n is the refractive index of the lens material, n₀ is therefractive index of the surrounding medium, R₁ and R₂ are the two radiiof curvature of the lens, and d is the thickness of the lens.

The importance of change in the refractive index is shown in FIG. 2,which is a graph showing the normalized change in lens optical power asa function of the refractive index for a lens placed both in water andair (normalized by the lens power at n=1.5). The calculations wereperformed using R₁=0.00185 m, R₂=0.00255 m, d=300 μm, n₀ forwater=1.3374, and n₀ for air=1.0000.

In some methods of the present disclosure, crosslinking is used tochange the refractive index of the lens. The lens thickness may eitherslightly shrink or increase, but the lens curvature is not appreciablyaltered. The primary change in lens optical power comes from the changein refractive index, not from the change in lens thickness or curvature.This is illustrated in FIG. 3. In FIG. 3A, the lens 100 contains apolymer matrix (denoted as P) having crosslinkable pendant groups(denoted as X). A mask 105 is used to expose only a portion 110 of thelens to UV or other radiation. As seen in FIG. 3B, crosslinking occursin the exposed portion 110 of the lens, changing the refractive index ofthe exposed portion.

A lens which is useful in this method may comprise a conventionalpolymer capable of behaving as a hydrogel, i.e. which can swell uponcontact with water. Typically, crosslinking a conventional polymerdecreases the volume of the polymer, similar to the decrease in volumeupon polymerization (i.e. a decrease in thickness occurs). Thisreduction in volume leads to an increased refractive index. However,there are monomers, such as3,9-divinyl-2,4,8,10-tetraoxy-spiro[5.5]undecane (shown below), whichexpand under photopolymerization.

Including similar functional groups as reactive sidechains or pendantgroups in the polymer may lead to an increase in volume uponcrosslinking. After crosslinking these functional groups, the regionswhere the polymer volume has increased will have decreased refractiveindex, while areas where the polymer volume decreases will haveincreased refractive index. Put another way, the crosslinked regions ofthe lens have increased refractive index.

Alternatively, crosslinking a hydrogel controls the degree to which itcan swell in the presence of water, preventing an increase in volume.After crosslinking, those regions where the hydrogel has beencrosslinked will have an increased refractive index compared to theregions where the hydrogel has not been crosslinked.

Because the change in lens optical power of such lenses does not rely ondiffusion of free monomers, the change in lens power can be monitored inreal time. Millan in Polymer 46 (2005), pp. 5556-5568, discloses acrosslinked polystyrene which increases refractive index and thicknessafter crosslinking.

One approach to approximate the role of crosslinking on the opticalproperties of polymers is to use the Lorentz-Lorenz formalism, whichexpresses the refractive index in terms of a molar refractivity R_(LL)and molar volume V, as in Equation 2:

$\begin{matrix}{n = \left\lbrack \frac{1 + {2\; {R_{LL}/V}}}{1 - {2\; {R_{LL}/V}}} \right\rbrack^{1/2}} & (2)\end{matrix}$

The effect of crosslinking is then treated as solely altering the molarvolume, without changing the molar refractivity. FIG. 4 shows the changein the refractive index associated with a change in the volume usingEquation 2. FIG. 5 shows the change in the lens power as a function ofthe change in volume. The calculations were performed using polymethylmethacrylate (PMMA) as the model compound, with MW=100.117,R_(LL)=24.754, and starting volume of V=865 (see van Krevelen,Properties of Polymers, 1976). The volume was systematically decreasedand the refractive index was calculated. The lens power calculationswere again performed using R₁=0.00185 m, R₂=0.00255 m, d=300 μm, n₀ forwater=1.3374, and n₀ for air=1.0000. The calculated refractive indexstarted at n=1.48415, and ended at n=1.50129 (Ln=0.01714, 1.15%).

FIG. 5 shows that a change of up to about 10% in lens optical power canoccur for a change in volume of less than about 3%, corresponding to athickness change in the lens of less than about 1%. The calculations arefairly insensitive to whether the volume change is modeled as justcorresponding to a thickness change, or is modeled as changing in all 3dimensions equally.

In embodiments, the lens suitable for practicing this method maycomprise a single polymer matrix containing crosslinkable pendantgroups, wherein the polymer matrix increases in volume when crosslinked.The lens does not contain free monomers that diffuse between regions toincrease the volume. Rather, the increase in volume is due to diffusionof water into the exposed (i.e. crosslinked) portion of the lens.

In embodiments, a method for altering the optical power of a lenscomprises providing a lens comprising a single polymer matrix havingcrosslinkable pendant groups, wherein the polymer matrix increases involume when crosslinked. The lens is devoid of, i.e. does not contain,free monomers. A portion of the lens is exposed to radiation, such asultraviolet radiation. This causes crosslinking to occur in the exposedportion of the lens and changes the refractive index of the exposedportion. The refractive index may increase or decrease, and decreases inparticular embodiments. In particular embodiments, the exposed portionis in the center of the lens.

In other methods of the present disclosure, ultraviolet (UV) radiationis used to photobleach the lens material. Certain aromatic groups, suchas naphthalene, can degrade under UV radiation exposure. This leads to adecrease in the refractive index in these exposed regions, without anychange in lens thickness. FIG. 6 is a schematic of the photobleachingprocess. In FIG. 6A, the lens 100 contains a polymer matrix (denoted asP) having photobleachable chromophores (denoted as C). A mask 105 isused to expose only a portion 110 of the lens to UV or other radiation.As seen in FIG. 6B, the chromophores in the exposed portion 110 of thelens are bleached (denoted as B), lowering the refractive index of theexposed portion compared to the unexposed portions 120, 130.Photobleaching has exceptional spatial resolution, commonly on the orderof a few microns. There is extensive literature on the design ofchromophores to photobleach and on the design of optical materials withenhanced photostability.

The photobleaching of a material can be described using Equation 3:

$\begin{matrix}{\frac{B}{\sigma} = {\tau \; n}} & (3)\end{matrix}$

where B is the probability of the degradation event happening, σ is thecross section, n is the photon flux, and τ is the lifetime of thechromophore. B/σ is often referred to as the photostabilityFigure-of-Merit (FOM). B/σ has strong energy dependence and also strongdependence on the maximum absorption wavelength (λ_(max)) of thechromophore.

The energy dependence can be approximated with Equation 4:

$\begin{matrix}{{\log \left\lbrack \frac{B}{\sigma} \right\rbrack} = {24 + {5.0 \times \left( {E_{\max} - E} \right)}}} & (4)\end{matrix}$

where E_(max), is the energy of the chromophore maximum absorptionwavelength.

The next step in the chromophore lifetime calculation is determinationof the maximum and average photon flux the lens will be exposed to. Thesolar spectrum has the form of FIG. 7, and is approximated by the solidline. Long wavelength radiation will be ignored in the determination, asit will have no effect on the photodegradation.

After conversion of the solar spectrum into photon flux, and using theenergy dependent FOM expression assuming chromophore absorption maximumof 325 nm, the plot of the chromophore lifetime as a function of theenergy in the solar spectrum can be obtained, and is shown as FIG. 8.The solid line is the chromophore lifetime, while the dotted line is thephoton flux.

The total chromophore lifetime is obtained from the summation of theinverse lifetimes (the total degradation rate is the sum of theindividual degradation rates). In this example, the total chromophorelifetime is calculated to be about 2.1×10⁵ seconds. Notably, there is arapid increase in lifetime as the wavelength increases. Much less than1% of the photodegradation in this example arises from wavelengthslonger than about 400 nm.

The previous calculation for the total chromophore lifetime assumes thatthe user stares directly into the noontime sun for the entire lenslifetime, which overestimates the total photon exposure during the lenslifetime. Using an ambient light level of 32,000 lux (average noontimelevel) for 9 hours, 9 hours of 400 lux (ambient office lighting) and 6hours of sleep per day, the photon flux is calculated to beoverestimated by a factor of 30, leading to a predicted lifetime for thelens of about 6.2×10⁶ seconds. This lifetime is still shorter thandesired (2×10⁹ seconds is desired), but literature precedent showsstraight-forward methods to increase the lifetime by more than the threeorders of magnitude needed.

The final issue is the amount of optical power available for thephotobleaching. Based on 2006 Trans. Am. Ophthalmol. Soc. p. 29, where apower of 12 mW/cm² was used for 120 seconds (A=365 nm), the photon fluxis 2.2×10²⁰/(m²·sec), and the total photon exposure is 2.7×10²²/m².Staring into the sun, the photon flux below 400 nm is 7.6×10¹⁹/(m²·sec),the ambient noontime flux below 400 nm is approximately2.5×10¹⁹/(m²·sec), and the average flux is 2.5×10¹⁸/(m²·sec).

In embodiments, a lens suitable for practicing this method comprises apolymer matrix containing photobleachable chromophores. The chromophoresmay be present as compounds dispersed within the polymer matrix or aspendant groups on the polymer matrix. The chromophores may contain areactive site which can react with a reactive site on the polymer matrixto allow crosslinking.

In particular embodiments, the chromophore contains a malononitrilemoiety. Exemplary chromophores include those of Formulas (I) and (II),which are also known as VC60 and EC24, respectively:

Formula (I) may also be called 4-morpholinobenzylidene malononitrile.Formula (II) may also be called2-[3-(4-N,N-diethylanilino)propenylidene] malononitrile.

In other embodiments, the chromophore is a stilbene compound of Formula(III):

where R₁-R₁₀ are independently selected from hydrogen, alkyl,substituted alkyl, aryl, substituted aryl, —COOH, and —NO₂.

The term “alkyl” as used herein refers to a radical which is composedentirely of carbon atoms and hydrogen atoms which is fully saturated.The alkyl radical may be linear, branched, or cyclic. Linear alkylradicals generally have the formula —C_(n)H_(2n+1).

The term “aryl” refers to an aromatic radical composed of carbon atomsand hydrogen atoms. When aryl is described in connection with anumerical range of carbon atoms, it should not be construed as includingsubstituted aromatic radicals. For example, the phrase “aryl containingfrom 6 to 10 carbon atoms” should be construed as referring to a phenylgroup (6 carbon atoms) or a naphthyl group (10 carbon atoms) only, andshould not be construed as including a methylphenyl group (7 carbonatoms). The term “heteroaryl” refers to an aryl radical which is notcomposed of entirely carbon atoms and hydrogen atoms, but rather alsoincludes one or more heteroatoms. The carbon atoms and the heteroatomsare present in a cyclic ring or backbone of the radical. The heteroatomsare selected from O, S, and N. Exemplary heteroaryl radicals includethienyl and pyridyl.

The term “substituted” refers to at least one hydrogen atom on the namedradical being substituted with another functional group selected fromhalogen, —CN, —NO₂, —COOH, and —SO₃H. An exemplary substituted alkylgroup is a perhaloalkyl group, wherein one or more hydrogen atoms in analkyl group are replaced with halogen atoms, such as fluorine, chlorine,iodine, and bromine. Besides the aforementioned functional groups, analkyl group may also be substituted with an aryl group. An aryl groupmay also be substituted with alkyl. Exemplary substituted aryl groupsinclude methylphenyl and trifluoromethylphenyl.

Generally, the substituents R₁-R₁₀ are selected to enhance otherproperties of the chromophore. For example, R₁, R₅, R₆, or R₁₀ could beselected to be a crosslinkable group, such as a carboxylic acid. Thesubstituents may also be selected as to control the absorption maximumand/or the refractive index of the chromophore, such as trifluoromethyl(to lower the refractive index), or a nitro group (to redshift theabsorption maximum). The substituents may also be selected to enhancethe photostability of the chromophore. For example, inclusion of a bulkygroup at the 2 or 2′ position, such as phenyl, inhibits trans-cisisomerization.

In other embodiments, the chromophore is an azobenzene compound ofFormula (IV):

where R₁₀-R₂₀ are independently selected from hydrogen, alkyl,substituted alkyl, aryl, substituted aryl, —COOH, —NO₂, halogen, amino,and substituted amino. Generally, the substituents R₁₀-R₂₀ are selectedto enhance other properties of the chromophore.

The term “amino” refers to —NH₂.

In still other embodiments, the chromophore must absorb more than onephoton for bleaching to occur. FIG. 9 provides an explanation. Asillustrated in FIG. 9A, the chromophore molecule has three energylevels, which include the ground state G, the first excited state Bwhich can be accessed from the ground state by the absorption of asingle photon ω_(max), and the second excited state A which cannot beaccessed from the ground state by a single photon absorption. Typically,there is an allowed transition between states B and A. The secondexcited state A is the state where the chromophore bleaches. Analysis ofthe one and two photon absorption spectra for simple chromophoresindicates that the energy of state B relative to the ground state isapproximately 0.85 of the energy of state A relative to the ground state(Marius Albota, Science 281, p. 1653 (1998)). FIG. 9B shows the energyspectrum for a standard two-photon absorption. In this process, twophotons w of the same wavelength are absorbed, when the energy of asingle photon is too small to be directly absorbed. In this case, theabsorption rate depends on the square of the optical intensity. It isalso possible to have a two photon absorption where the two photons areof different frequencies. This is shown in FIG. 9C, where two distinctphotons ω1 and ω2 are absorbed, even though neither photon alone hassufficient energy to excite the molecule to even the first excited stateB. In this case, the absorption intensity is proportional to the productof the intensity of each wavelength.

In embodiments, a method for altering the optical power of a lenscomprises providing a lens comprising a polymer matrix containingphotobleachable chromophores. A portion of the lens is exposed toradiation, such as ultraviolet radiation. This causes photobleaching tooccur in the exposed portion of the lens and changes the refractiveindex of the exposed portion. The refractive index may increase ordecrease, and decreases in specific embodiments. In particularembodiments, the exposed portion is in the center of the lens.

After the optical power of the lens is altered, the lens must bestabilized to prevent further undesired changes. Previous lenses whichinclude free monomer(s) typically used partial polymerization, allowedthe free monomer(s) to diffuse, then did a complete polymerization topreclude any further change in the shape of the lens or the refractiveindex. The present disclosure contemplates at least three methods ofstabilization.

First, a UV radiation absorbing layer may be laid over at least onesurface of the lens. The UV radiation absorbing layer ideally almostcompletely absorbs short wavelength photons at low UV intensity, butpasses most photons at high UV intensity. An exemplary lens is shown inFIG. 10. Here, the lens 200 comprises a polymer matrix 210 and UVradiation absorbing layers 220, 230 on each surface 212, 214 of thepolymer matrix. An idealized transmission spectrum at the bleachingwavelength and longer is shown in FIG. 11. At wavelengths shorter thanthe bleaching wavelength, the UV absorption layer completely absorbsphotons. At the bleaching wavelength and longer, however, the photonabsorption depends on the incident flux. At low levels of incident UVintensity, i.e. that of natural illumination, the transmitted flux (i.e.the number of photons passing through the UV absorption layer) is low orzero. At higher levels of incident UV intensity, however, i.e. appliedillumination, the transmitted flux increases. This difference allows thelens to be adjusted after implantation by the application of artificialradiation, then prevent further adjustment during natural use. This UVabsorbing layer can be used with both types of lenses described above.

The second stabilization method involves crosslinking the chromophore tothe polymer matrix, through for example the 2′ position. The chromophorecan be attached to the polymer matrix as a pendant group or sidechainwith a reactive site or group on the chromophore, and a correspondingreaction site or group elsewhere on the polymer matrix. Afterfabrication, the lens can be stored at a temperature below the Tg of thepolymer, greatly slowing the crosslinking reaction. After implantation,the chromophore will slowly crosslink with the polymer matrix, greatlyenhancing its photostability. The rate of this crosslinking reaction canbe controlled by altering the functionality of the reactive groups,allowing sufficient time for the lens to be adjusted. If thecrosslinking occurs through a condensation reaction, water will be theonly by-product. After crosslinking, there will be a further reductionin the rate at which the isomerization can occur, further enhancingphotostability.

Crosslinking the chromophore through its 2′ position is significantbecause of the degradation mechanism of, for example, stilbenechromophores. The primary degradation pathway of stilbene chromophoresis through oxidation of the central double bond after a trans-cisisomerization. Thus, blocking groups have also shown an increase in thechromophore stability. As shown in the following diagram, theunsubstituted stilbene can undergo trans-cis isomerization, while thesubstituted stilbene is sterically hindered. By hindering isomerization,stability is increased.

Finally, the third stabilization method uses a chromophore whichbleaches under specific conditions. In particular, a chromophore whichrequires the absorption of more than one photon to bleach is used. Thebleaching process is slow under low-level illumination, but may stilloccur, particularly during daytime outside exposure. However, judiciousselection of the excitation wavelengths of the chromophore can slow thisprocess even further. Referring back to FIG. 7, certain wavelengths arefiltered from the solar spectrum, due to the presence of specificcompounds in the atmosphere. Design of the chromophore so that one ofthe two wavelengths needed to cause bleaching corresponds to one of thefiltered wavelengths will lead to a lens with enhanced stability, asthere will be no high-intensity natural radiation at that wavelength toinitiate the photodegradation.

For example, if we assume a chromophore with an absorption maximum of400 nm, the two-photon absorption would then occur at about 340 nm. Ifone of the wavelengths is 1300 nm (which is strongly absorbed in theatmosphere), we can the calculate that the other wavelength needed wouldbe 460 nm. Thus a combination of a 1300 nm photon and a 460 nm photoncould be absorbed, even though neither photon will be absorbedindividually. Because the 1300 nm photon is not strongly present innatural outdoor illumination, absorption and continued photobleachingwould not occur.

The photostability of chromophores may also be enhanced in other ways.The chromophores may be attached to the polymer matrix as a polymer sidechain or pendant group. Chromophores could be crosslinked to otherfunctional groups on the polymer backbone or sidechains, reducing theconformational movement often needed as part of the photobleachingprocess. The absorption maximum wavelength could be blue-shifted. Thefunctional groups of the chromophore could be changed to inhibitrotational motion around specific bonds, or block specificphotodegradation pathways. For example, inclusion of a trifluoromethylgroup at the 2 or 2′ position of an azobenzene chromophore can reducethe rate at which photobleaching occurs. Finally, the local environmentof the chromophore could be changed, e.g. by changing the local pH.

Several other methods of altering the optical power of a lens are alsodisclosed. These methods relate to lenses that use photobleachablechromophores and a polymer matrix. Generally, exposure to radiation isused to cause bleaching with different variations.

In some methods, the lens includes a polymer matrix havingphotobleachable chromophores and a photosensitive donor lackingphotoinitiating groups. This system uses a two-photon process. In otherwords, the donor needs to absorb two photons to have sufficient energyto degrade the chromophores, which causes photobleaching and changes therefractive index.

The donor molecule is responsive to a first photon and generates primaryexcited state donor molecules which are not responsive to the firstwavelength of energy. However, the primary excited state donor moleculesare responsive to a sequentially applied second photon that generatessecondary higher energy level excited state donor molecules.

The chromophores have a lowest primary excited state energy greater thanthe primary excited state energy of the photosensitive donor molecules.Thus, the chromophores cannot receive energy from the primary excitedstate donor molecules that would cause degradation. Only when secondaryhigher energy level excited state donor molecules are generated can thechromophores accept energy to reach an excited state that causesdegradation of the chromophore. This results in photobleaching and therefractive index to be changed, thus altering the optical power of thelens.

The two photons absorbed by the donor may be of the same wavelength(degenerate) or of different wavelengths (non-degenerate). In regard tothe non-degenerate method, it is contemplated that a first portion ofthe lens is exposed to radiation at the first wavelength, and a secondportion of the lens is exposed to radiation at the second wavelength.The second portion completely overlaps the first portion, or in otherwords the first portion can be of a larger area than the second portion.

The photosensitive donor may be selected from chromophores with largedegenerate two-photon absorption such as those illustrated in Formulas(A)-(E):

wherein each Ar is an aryl or substituted aryl; each R is alkyl; and nreflects the number of double bonds in the conjugated bridge and can befrom 1 to 4.

In some embodiments, two or more photosensitive donors are included inthe lens. The photosensitive donor(s) may be present in the lens in anamount of from about 0.05 to about 5 wt % of the lens.

In some embodiments, the chromophores may be selected from the groupconsisting of naphthalene sulfonyl chloride, quinolone sulfonylchloride, and alpha-chloromethyl naphthalene. The chromophores may bepresent in the lens in an effective amount.

The first wavelength may be from about 1500 nm to about 350 nm. When thechromophore absorbs photons of different wavelengths, the secondwavelength may also be from about 1500 nm to about 350 nm, but isdifferent from the first wavelength.

In some other methods, a lens including a polymer matrix havingphotobleachable chromophores is used. A portion of the lens is exposedto non-visible radiation, causing photobleaching to occur in the exposedportion of the lens and changing the refractive index of the exposedportion of the lens, thereby altering the optical power of the lens. Thelens may be a contact lens.

The non-visible radiation may be selected from gamma radiation, X-rayradiation, and ultraviolet radiation. In some embodiments, thenon-visible radiation is provided by an excimer laser.

In some variations on this method, a portion of the lens is exposedinstead to electromagnetic or charged particle radiation, causingphotobleaching to occur in the exposed portion of the lens and changingthe refractive index of the exposed portion of the lens, therebyaltering the optical power of the lens. In some embodiments, the chargedparticle radiation is provided by an electron beam. The lens may be acontact lens.

In some other methods, a lens is provided that includes a single polymermatrix having crosslinkable pendant groups. The polymer matrix does notchange significantly in volume when crosslinked. A portion of the lensis exposed to electromagnetic or charged particle radiation, causingcrosslinking to occur in the exposed portion of the lens and changingthe refractive index of the exposed portion of the lens, therebyaltering the optical power of the lens.

The lens may be devoid of free monomers. In some embodiments, thecharged particle radiation is provided by an electron beam.

Some methods comprise providing a lens including a polymer matrixcontaining a first chromophore and a second, different chromophore. Thefirst chromophore acts as a photoinitiator or catalyst for bleaching thesecond chromophore, which causes the subsequent change in the refractiveindex of the lens. A portion of the lens is exposed to radiation,causing photobleaching to occur in the exposed portion of the lens andchanging the refractive index of the exposed portion of the lens,thereby altering the optical power of the lens.

Two variations on this method are contemplated. First, the secondchromophore is only bleached by the first chromophore, or in other wordsthe second chromophore is not sensitive to the radiation. Second, theradiation causes the first chromophore to change from an inactive stateto an active state. In the inactive state, the first chromophore doesnot bleach the second chromophore. In the active state, though, thefirst chromophore can act as a photoinitiator or catalyst for the secondchromophore. The second chromophore is sensitive to both the radiationand to the first chromphore. In other words, bleaching of the secondchromophore is faster than would be expected without the firstchromophore.

The first chromophore may be selected from aromatic or aliphaticphotoinitiators, or aromatic ketones such as benzophenone andthioxanthone. The first chromophore may be present in the lens in anamount of from about 0.05 to about 5 wt %. Exemplary first chromophoresinclude Irgacure® molecules available from Ciba, such as1-hydroxy-cyclohexyl-phenylketone (Irgacure® 184);2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one(Irgacure® 127);2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-propanone (Irgacure®2959); bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure® 819);2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (Irgacure®907); 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one(Irgacure® 369);2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one(Irgacure® 379); and 2,2-dimethoxy-1,2-diphneylethan-1-one (Irgacure®651).

In some embodiments the benzophenone is a compound of Formula (V):

wherein R₂₁-R₃₀ are independently selected from hydrogen, alkyl,substituted alkyl, aryl, substituted aryl, —COOH, —NO₂, halogen, amino,and substituted amino. In some embodiments, R₂₁-R₃₀ are hydrogen.

In some embodiments the thioxanthone is a compound of Formula (VI):

wherein R₃₁-R₃₈ are independently selected from hydrogen, alkyl,substituted alkyl, aryl, substituted aryl, —COOH, —NO₂, halogen, amino,and substituted amino. In some embodiments, R₃₁-R₃₈ are hydrogen.

The second chromophore may be selected from C.I. Solvent Blue 101; C.I.Reactive Blue 246; C.I. Pigment Violet 23; C.I. Vat Orange 1; C.I. VatBrown 1; C.I. Vat Yellow 3; C.I. Vat Blue 6; C.I. Vat Green 1; C.I.Solvent Yellow 18; C.I. Vat Orange 5; C.I. Pigment Green 7; D&C GreenNo. 6; D&C Red No. 17; D&C Yellow No. 10; C.I. Reactive Black 5; C.I.Reactive Blue 21; C.I. Reactive Orange 78; C.I. Reactive Yellow 15; C.I.Reactive Blue 19; C.I. Reactive Blue 4; C.I. Reactive Red 11; C.I.Reactive Yellow 86; C.I. Reactive Blue 163; and C.I. Reactive Red 180.The second chromophore may be present in the lens in an amount of fromabout 0.5 to about 20 wt.

In still other methods, the lens comprises a polymer matrix having achromophore. The lens is in proximity to a photoactivated bleachingcatalyst. For example, the lens and the bleaching catalyst may becombined in a package, or the bleaching catalyst can be dispersed in thelens. Upon exposure to radiation, the bleaching catalyst causesphotobleaching to occur in at least a portion of the lens, changing therefractive index of the exposed portion of the lens, thereby alteringthe optical power of the lens.

The photoactivated bleaching catalyst may be selected fromperoxide-generating materials, singlet-oxide generating materials, andozone-generating materials. Exemplary peroxide-generating materials areknown in the art. Exemplary singlet-oxide generating materials includeare known in the art. Exemplary ozone-generating materials include areknown in the art.

Finally, it is contemplated that the lens can include a polymer matrixhaving photobleachable chromophores; and initiating a reaction tophotobleach the chromophores. The reaction is selected from the groupconsisting of an oxidation or reduction reaction, a catalytic acid orbase reaction, a dimerization reaction, a molecular rearrangementreaction, a free radical propagation reaction, a free radicalnon-propagation reaction, a reaction changing the number of unsaturationsites, a charge transfer reaction, and a chromophore modificationreaction.

The concept of controlling the refractive index of a material withoutchanging its shape allows a lens to be fabricated into a uniform sheetof polymer that has been doped with suitable chromophores. This allowsthe creation of a Fresnel lens from a sheet of material that is smoothand much easier to fabricate and clean. This lens could be used inphotovoltaic applications, where cleaning of mirrors and photovoltaicsurfaces is the largest portion of the operations budget. Alternately alens could be created in a panel or window to allow for control of lightpassing through the window or panel. This could be used forarchitectural or design purposes, or alternately may have applicationsin controlling light passing through the panel.

Use of the various methods described above are also specificallycontemplated for use with intraocular lenses and with contact lenses.Contact lenses are generally made from biocompatible polymers which donot damage the ocular tissue and ocular fluid during the time ofcontact. In this regard, it is known that the contact lens must allowoxygen to reach the cornea. Extended periods of oxygen deprivationcauses the undesirable growth of blood vessels in the cornea. “Soft”contact lenses conform closely to the shape of the eye, so oxygen cannoteasily circumvent the lens. Thus, soft contact lenses must allow oxygento diffuse through the lens to reach the cornea.

Another ophthalmic compatibility requirement for soft contact lenses isthat the lens must not strongly adhere to the eye. The consumer must beable to easily remove the lens from the eye for disinfecting, cleaning,or disposal. However, the lens must also be able to move on the eye inorder to encourage tear flow between the lens and the eye. Tear flowbetween the lens and eye allows for debris, such as foreign particulatesor dead epithelial cells, to be swept from beneath the lens and,ultimately, out of the tear fluid. Thus, a contact lens must not adhereto the eye so strongly that adequate movement of the lens on the eye isinhibited.

Suitable materials for contact lenses are well known in the art. Forexample, polymers and copolymers based on 2-hydroxyethyl methacrylate(HEMA) are known, as are siloxane-containing polymers that have highoxygen permeability, as well as silicone hydrogels. Any suitablematerial can be used for the polymer matrix of a contact lens to whichthe methods described herein can be applied.

Aspects of the present disclosure may be further understood by referringto the following examples. The examples are merely for furtherdescribing various aspects of the devices and methods of the presentdisclosure and are not intended to be limiting embodiments thereof.

EXAMPLES

Experimental measurements were performed to verify that the refractiveindex changed upon crosslinking and without the presence of freemonomer. The experiments also showed that the refractive index changewas controllable, reproducible, and adjustable.

A series of experiments were also performed to verify the amount ofchange in the refractive index possible with photobleaching, and alsothat photobleaching could occur in an aqueous environment.

Example 1

A solution of 37.5% SARTOMER CN990, 59.4% SARTOMER SR344 and 3.1%DAROCUR 4265 was created (composition was based on weight fraction ofthe components). SARTOMER CN990 is a siliconized urethane acrylateoligomer. SARTOMER SR344 is a polyethylene glycol diacrylate having amolecular weight of 508. DAROCUR 4265 is a photoinitiator mixture of 50weight percent diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide and 50weight percent 2-hydroxy-2-methyl-1-phenyl-1-propanone. DAROCUR 4265 hasabsorption peaks at 240, 272, and 380 nm in methanol.

The refractive index of the solution was measured to be 1.4717. Thesolution was then cast onto a slide and exposed to 10 seconds of UVlight from a lamp source. The refractive index of the film was thenmeasured using a Metricon Model 2010 Prism Coupler, and was determinedto be 1.4747. Additional UV exposure of 5 seconds gave a refractiveindex of n=1.4852. Further UV exposure of 15 seconds gave a refractiveindex of n=1.4868. In other words, as the amount of UV exposureincreased, the amount of crosslinking increased and thus the refractiveindex increased.

Example 2

The solution of Example 1 was again created, except the DAROCUR 4265 wasreplaced with IRGACURE 2959, which is sensitive to 254 nm UV. Thesolution was cast onto a plate and exposed to UV light. After 2 secondsexposure, the refractive index was measured with the prism coupler andfound to be n=1.4668, with the film not being fully cured in the center.An additional 5 second UV exposure led to the refractive index beingmeasured as n=1.485.

Example 3

A third experiment was performed to better evaluate theexposure-dependence of the refractive index. A solution similar to thatof Example 1 was prepared and cast onto a slide. The film then underwentseveral cycles of UV exposure and refractive index measurement. Theresults are shown in FIG. 12. Below 8 seconds exposure, the film was notfully set. The data is also summarized in Table 1.

TABLE 1 Time (sec) Refractive Index 8 1.4799 10 1.4804 15 1.4835 201.4887 25 1.489

The results indicated that the refractive index could be changed by arange of about 0.01 after exposure of about 25 seconds. This value ofindex change was selected as providing approximately a 10% change inlens power (as shown in FIG. 2).

Example 4

A solution of VC60 in polymethylmethacrylate (PMMA) was cast as a filmand dried at 80° C. for 10 minutes. The refractive index of the film was1.4909. The film was then exposed to 254 nm radiation for 1 minute. Therefractive index was then measured to be 1.5016. After further exposure(30 minutes total) the refractive index was 1.5036. Absorbancemeasurements showed ˜50% decrease in absorbance due to the chromophore.

Example 5

A solution of EC24 in PMMA was cast as a film and dried at 80° C. for 10minutes. The refractive index of the film was measured as n=1.5014. Thefilm was then exposed to 254 nm radiation for 30 minutes. The refractiveindex was then measured as n=1.4924.

Example 6

EC24 was then diffused into an ACUVUE lens (Johnson & Johnson VisionCare, Inc.). The lens was partially masked, then exposed to 254 nm UVlight for 30 minutes. The chromophore bleached, but over time thedemarcation line between the masked and unmasked portions of the lensblurred. This may be attributable to migration of the chromophore in thelens.

The experiment was then repeated by diffusing EC24 into two separateACUVUE lenses. The first lens was kept as a control, and exhibited veryuniform red color, consistent with an absorption maximum near 510 nm forEC24 in the lens. The second lens was exposed to the UV light for 30minutes. At the end of this exposure, the second lens exhibited no colorand was completely transparent.

Example 7

The transmission spectra of an ACUVUE lens was measured. EC24 was thendiffused into the lens, and the transmission spectrum was measuredagain. Finally, the lens was bleached and the transmission spectrum wasmeasured a third time. The results are shown in FIG. 13 and Table 2.

TABLE 2 % T EC24 % T Wavelength (nm) % T hydrated lens doped lensbleached lens 350 10.3 4.5 21 360 10.7 11.7 19.4 370 28.4 30.1 36.4 38063.9 52.6 60.9 390 82.5 62 72.1 400 87 64 72.8 410 87.9 64.4 75.9 42088.3 64.5 76.4 430 88.4 64.5 76.7 440 88.8 64.2 77.2 450 88.8 64.1 77.6460 89 63.5 77.6 470 89 62.6 77.8 480 89.1 61.9 78.7 490 89.2 61.3 80500 89.1 60.6 81.2 510 88.9 60.3 81.6 520 88.8 60.6 82.2 530 88.8 61.182.7 540 88.9 62.4 83.5 550 88.9 64.1 83.9 560 88.9 66.2 84.5 570 88.967.8 84.9 580 88.9 69.3 85.5 590 88.8 70 86 600 89 70.6 86.6

Note that the EC24 doped lens shows a transmission minimum close to 510nm, while the absorption maximum of EC24 in dioxane was measured to be503 nm. This indicates that the EC24 is present in the doped lens. Thephotobleached lens has weaker absorption and no longer has theabsorption at 510 nm, indicating that the photobleaching process hasaltered the chemistry of EC24.

The devices and methods of the present disclosure have been describedwith reference to exemplary embodiments. Obviously, modifications andalterations will occur to others upon reading and understanding thepreceding detailed description. It is intended that the exemplaryembodiments be construed as including all such modifications andalterations insofar as they come within the scope of the appended claimsor the equivalents thereof.

1. A method of altering the optical power of a lens, comprising:providing a lens comprising: a polymer matrix having photobleachablechromophores; and a photosensitive donor lacking photoinitiating groupsand responsive to a first selective wavelength of energy for generatingprimary excited state donor molecules which are not responsive to saidfirst selective wavelength, but are responsive to sequentially appliedsecond selective wavelengths of energy for generating secondary higherenergy level excited state donor molecules; the chromophores having alowest primary excited state greater than the primary excited state ofthe photosensitive donor, the secondary higher energy level excitedstate of the photosensitive donor molecules being greater than thelowest primary excited state of the chromophores; and exposing a portionof the lens to radiation at the first selective wavelength to generateprimary excited state donor molecules; and exposing the exposed portionof the lens to radiation of the second selective wavelength to generatesecondary higher energy level excited state donor molecules, causingphotobleaching to occur in the exposed portion of the lens and changingthe refractive index of the exposed portion of the lens, therebyaltering the optical power of the lens.
 2. The method of claim 1,wherein the lens is a contact lens.
 3. The method of claim 1, whereinthe photosensitive donor is selected from the group consisting ofFormulas (A)-(E):

wherein each Ar is an aryl or substituted aryl; each R is alkyl; and nreflects the number of double bonds in the conjugated bridge and can befrom 1 to
 4. 4. The method of claim 1, wherein the chromophores areselected from the group consisting of naphthalene sulfonyl chloride,quinolone sulfonyl chloride, and alpha-chloromethyl naphthalene.
 5. Themethod of claim 1, wherein the first and second wavelengths aredifferent.
 6. A method of altering the optical power of a lens,comprising: providing a lens comprising a polymer matrix havingphotobleachable chromophores; and exposing a portion of the lens tonon-visible radiation, causing photobleaching to occur in the exposedportion of the lens and changing the refractive index of the exposedportion of the lens, thereby altering the optical power of the lens. 7.The method of claim 6, wherein the non-visible radiation is selectedfrom the group consisting of gamma radiation, X-ray radiation, andultraviolet radiation.
 8. The method of claim 6, wherein the non-visibleradiation is provided by an excimer laser. 9-13. (canceled)
 14. A methodof altering the optical power of a lens, comprising: providing a lenscomprising a polymer matrix containing a first chromophore and a secondchromophore; and exposing a portion of the lens to radiation, causingphotobleaching to occur in the exposed portion of the lens and changingthe refractive index of the exposed portion of the lens, therebyaltering the optical power of the lens; wherein the first chromophore issensitive to the radiation and is a photoinitiator or catalyst forbleaching the second chromophore.
 15. The method of claim 14, whereinthe second chromophore is not sensitive to the radiation but issensitive to the first chromophore.
 16. The method of claim 14, whereinthe first chromophore is transformed from an inactive state to an activestate by the exposure to the radiation.
 17. The method of claim 14,wherein the first chromophore is an aromatic ketone.
 18. The method ofclaim 14, wherein the first chromophore is present in an amount of fromabout 0.05 to about 5 wt %; and wherein the second chromophore ispresent in an amount of from about 0.5 to about 20 wt %.
 19. The methodof claim 17, wherein the second chromophore is selected from the groupconsisting of C.I. Solvent Blue 101; C.I. Reactive Blue 246; C.I.Pigment Violet 23; C.I. Vat Orange 1; C.I. Vat Brown 1; C.I. Vat Yellow3; C.I. Vat Blue 6; C.I. Vat Green 1; C.I. Solvent Yellow 18; C.I. VatOrange 5; C.I. Pigment Green 7; D&C Green No. 6; D&C Red No. 17; D&CYellow No. 10; C.I. Reactive Black 5; C.I. Reactive Blue 21; C.I.Reactive Orange 78; C.I. Reactive Yellow 15; C.I. Reactive Blue 19; C.I.Reactive Blue 4; C.I. Reactive Red 11; C.I. Reactive Yellow 86; C.I.Reactive Blue 163; and C.I. Reactive Red
 180. 20. (canceled)
 21. Amethod of altering the optical power of a lens, comprising: receiving apackage in which a lens comprising a polymer matrix having bleachablechromophores is in proximity with a photoactivated bleaching catalyst;and exposing the package to radiation, causing photobleaching to occurin the lens, changing the refractive index of at least a portion of thelens, thereby altering the optical power of the lens.
 22. The method ofclaim 21, wherein the photoactivated bleaching catalyst is selected fromthe group consisting of a peroxide-generating material, a singletoxide-generating material, and an ozone-generating material.
 23. Amethod of altering the optical power of a lens, comprising: providing alens comprising a polymer matrix having a photobleachable chromophore;and initiating a reaction to photobleach the chromophore; wherein thereaction is selected from the group consisting of an oxidation orreduction reaction, a catalytic acid or base reaction, a dimerizationreaction, a molecular rearrangement reaction, a free radical propagationreaction, a free radical non-propagation reaction, a reaction changingthe number of unsaturation sites, a charge transfer reaction, and achromophore modification reaction.